This is the first Dummies book I've read, and I liked it more than I expected. The content is educational and the style is matter-of-fact. It really does try to cover something approaching the full scope of geology including mineral types, rock types, processes in the rock cycle, transport and deposition of sediments, plate tectonics, and even paleontology. Because the scope was so broad, the depth was intrinsically relatively shallow. There were several subjects I was not very interested in (e.g. I've already read much more deeply in paleontology and wasn't looking for a high level primer as provided in this book), and there were other subjects where this book presents the "what" but left me wishing to better understand the "why."
The main thing I wanted to get out of this book was a better understanding of the classification of minerals and rocks. Unfortunately, this subject is complex, so I still don't understand it very well. However, this book did at least help me understand why I find it so confusing. The scheme used to classify rocks is not exactly consistent or systematic. Some rock types refer to mineral content, some to particle sizes, some to formation type, and some even to location (e.g. above or below the surface). Therefore, you can't just line up all rocks along some spectrum and classify them by one particular characteristic.